Substantial quantities of titanium dioxide pigment are produced commercially by reacting titanium tetrachloride with oxygen in the vapor phase. Immediately after such reaction, the titanium dioxide reaction mass is cooled by passing it through a conduit, i.e., flue, where growth of the titanium dioxide pigment particles takes place and agglomeration of such particles takes place.
It is desirable to cool the titanium dioxide rapidly because this will result in pigment having higher carbon black undertone ("CBU"). CBU is described in U.S. Pat. No. 2,488,440, which is hereby incorporated by reference. However, when a smaller diameter flue is used to permit more rapid cooling, it has been found that while CBU is increased, turbulence can be increased, which increases agglomeration of the pigment particles and thereby decreases pigment gloss.
Also, it would be desirable to operate titanium dioxide processes at higher pressures to minimize equipment expenditures, but this can decrease CBU. Moreover, it is desirable to increase TiO.sub.2 output, but higher product output can decrease CBU (due to the increased pressure) and decrease gloss (due to the increased turbulence).
The following information is disclosed which may be of interest to this invention.
U.S. Pat. No. 3,273,599 discloses an internally finned condenser tube.
U.S. Pat. No. 2,833,627 discloses a method for cooling TiO.sub.2 by passing it through a water-cooled conduit.
U.S. Pat. No. 4,462,979 discloses a method for cooling and producing TiO.sub.2 having improved agglomerating properties, which comprises first increasing the cross-sectional area of the flue and then decreasing the cross-sectional area of the flue.